Interest of the Study of the Influence of Ocular Fixation during Caloric Tests in Pontocerebellar Tumors

Abstract

Measurement of the ocular fixation index is very useful to assess the extension of pontocerebellar tumors. Determination of the other features of central impairment of the vestibular system completes this information.

Cerebellopontine Angle Tumors: Bilateral Flocculus Compression as Cause of Associated Oculomotor Abnormalities

“…Reduced afferent input from a vestibular nerve onto the vestibular nuclei from a small acoustic neuroma is fully compensated because both flocculi are healthy and the flocculus of the side opposite the t?r:ior can re-set the vestibular spike discharge ac-t1v1ty to a reduced level to match the lowered activity of the nuclei on the tumor side.4 8 Nystagmus is therefore absent. ·…”

Unsteadiness of cerebellar origin: An investigation into its cause

“…Some measure of this effect may be obtained by recording the nystagmic response to the caloric irrigation beginning with eyes closed and then at some point near the culmination of the response requiring the patient to open his eyes for a short period and fixate a target. The relative magnitudes of the nystagmic responses immediately prior to and during fixation are expressed as a fixation index (Demanez and Ledoux, 1970;Corvera et ah, 1968;Boniver and Demanez, 1977) and provide a measure of the inhibitory effect of optic fixation. Earlier measurements of this kind can be criticized on a number of counts, not least of which is the absence of any direct information on the overall responses with and without optic fixation.…”